Field of the Invention
The present invention relates to composite modules including circuit boards on which a plurality of communication systems that communicate using the respective predetermined frequency bands are provided.
Description of the Related Art
Cellular phone terminals configured to be capable of communicating through a plurality of communication standards, such as GSM® (Global System for Mobile Communications), PDC (Personal Digital Cellular), PCS (Personal Communications Service), and CDMA (Code Division Multiple Access), are being provided in recent years. Recently, mobile information terminals such as laptop computers, smartphones, and so on are also being configured to be capable of communicating through a plurality of wireless LAN standards, as typified by IEEE 802.11a/b/g/n or the like. A mobile communication terminal such as a cellular phone terminal or a mobile information terminal that is compliant with a plurality of communication standards in this manner includes a composite module having a circuit board in which a plurality of communication systems, which communicate using the respective predetermined frequency bands defined by those standards, are provided.
A demultiplexing circuit, a switching circuit, and the like for supplying a communication signal (RF signal), which is in a predetermined frequency band inputted from the exterior, to the communication system corresponding to that RF signal, an amplifying circuit such as a power amplifier (PA), a low-noise amplifier (LNA), and the like for amplifying signals inputted from the exterior, signals outputted to the exterior, and so on, are provided on the circuit board of a composite module in which a plurality of communication systems are provided. Meanwhile, mobile communication terminals are becoming smaller in size, and as such, the high-frequency circuit components installed in mobile communication terminals, such as those described above, are also becoming smaller and more highly integrated. Furthermore, the high-frequency circuit components of which each communication system is configured are disposed in close proximity on the circuit board, wiring electrodes that connect the high-frequency circuits provided in each communication system and form signal paths for the RF signals are disposed in close proximity, and so on.
Due to such proximate disposal, there is a risk that the isolation characteristics between the communication systems and the high-frequency circuits will degrade. There is a further risk that the RF signal amplified by the amplifying circuit entering an antenna switching circuit, which includes a demultiplexing circuit, a low-pass filter, and the like, will result in signal loss in the demultiplexing circuit, the antenna switching circuit, and so on, and that the RF signal flowing through the antenna switching circuit entering the amplifying circuit will cause the amplifying circuit to oscillate and become unstable. There has also been a risk that the RF signals in the respective communication systems will interfere with each other and degrade the communication quality in the communication systems.
Accordingly, thus far, a plurality of through-hole electrodes connected to ground electrodes have been provided in locations, of the circuit board on which the composite module is provided, where superior isolation characteristics are required, such as between the respective communication systems, the respective high-frequency circuits, and the respective wiring electrodes that form signal paths through which RF signals pass, in order to prevent the isolation characteristics from degrading between the respective communication systems, the respective high-frequency circuits, and the respective signal paths (see Patent Document 1, for example). For example, a conventional composite module 500 shown in FIG. 4 includes a circuit board 501 within which a plurality of wiring electrodes are provided and a plurality of electrical components 502 mounted on a component mounting surface 501a of the circuit board 501; here, wiring electrodes that configure an amplifying circuit are formed on a left-side region of the circuit board 501, and wiring electrodes that configure a switching circuit are formed on a right-side region of the circuit board 501.
Furthermore, a shield electrode 503 is provided on the component mounting surface 501a of the circuit board 501, at a border between the left-side region in which the amplifying circuit is provided and the right-side region in which the switching circuit is provided, and a plurality of through-hole electrodes 504 that are connected to the shield electrode 503 and that are formed in the layering direction of the circuit board 501 are provided in tandem along the depth direction in FIG. 4. By connecting the through-hole electrodes 504 to a plurality of ground electrodes 505 provided within the circuit board 501, the RF signals are suppressed from interfering with each other between the amplifying circuit provided in the left-side region of the circuit board 501 and the switching circuit provided in the right-side region of the circuit board 501.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-151123 (paragraph 0043, FIG. 4, abstract, etc.)